1. Field of the Invention
This invention relates generally to a storage tank system for storing a high pressure gas and, more particularly, to a storage tank system for storing a high pressure gas, where the tank system includes a master tank having a master tank shut-off valve and at least one slave tank having a slave tank shut-off valve, and where the slave tank shut-off valve has a low pressure differential so that a rupture or leak will cause it to automatically close.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cells as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines. In an automotive fuel cell application, the hydrogen fuel is sometimes stored in a high pressure tank system on the vehicle. In one particular design, the tank system includes a master tank and at least one slave tank.
FIG. 1 is a schematic plan view of a compressed hydrogen gas master/slave tank system 10 of a type known in the art for this purpose. The tank system 10 includes a master tank 12 and a slave tank 14. A valve protection filter 16 is positioned within the master tank 12 so that fuel from the tank 12 flowing through an output line 18 to a fuel cell stack (not shown) is free of contaminants. The pressure within the master tank 12 and the slave tank 14 may be upwards of 70 MPa. A first high pressure regulator 20 and a second high pressure regulator 22 are positioned in the line 18, where the regulators 20 and 22 reduce the pressure of the hydrogen gas in the tank 12 in steps to a usable pressure by the fuel cell stack. A low pressure electrically driven solenoid shut-off valve 24 is positioned in the line 18 downstream from the pressure regulators 20 and 22, where the valve 24 closes off the line 18.
When hydrogen gas is drawn from the master tank 12 during operation of the fuel cell stack, it is replenished by hydrogen gas from the slave tank 14 on line 30 so that the pressure within the tanks 12 and 14 remains substantially the same. A flow controller 32 is positioned within the line 30 to control the flow of the hydrogen gas from the slave tank 14 to the master tank 12. The flow controller 32 remains open unless the gas flow exceeds a predetermined maximum flow rate, possibly indicating a leak or rupture in the line 30, where the controller 32 will be closed. A manual shut-off valve 34 is positioned within the line 30 downstream from the flow controller 32 so that the tank 14 can be manually shut off to prevent hydrogen gas from flowing therefrom for servicing and the like.
A thermal activated pressure release valve 40 is positioned within a line 42 that is coupled to the master tank 12, and a thermal activated pressure relief valve 44 is positioned within a line 46 that is coupled to the slave tank 14. The valves 40 and 44 are normally closed, but are automatically opened if the temperature around the master tank 12 and the slave tank 14, respectively, exceeds a predetermined maximum temperature. Particularly, if the temperature does exceed the predetermined maximum temperature, the valves 40 and 44 are automatically opened to release the pressure within the tanks 12 and 14 to the environment for safety purposes.
When the tanks 12 and 14 need to be refueled, a refueling line (not shown) is coupled to a refueling coupler 50. The hydrogen gas flows from the refueling coupler 50 into a line 52 through a filter 54 that removes particulates therefrom. The line 52 is coupled to the line 30 so that both the master tank 12 and the slave tank 14 are simultaneously filled with the hydrogen gas. A check valve 56 in the line 52 prevents backflow of the hydrogen gas into the coupler 50 when the slave tank 14 is supplying the master tank 12 with hydrogen gas during operation of the fuel cell stack. Further, a check valve 58 in the line 30 prevents the hydrogen gas from flowing through the line 30 from the master tank 12.
As discussed above, the low pressure shut-off valve 24 is positioned downstream of the pressure regulators 20 and 22 in a low pressure part of the line 18. The slave tank 14 does not include a solenoid operated shut-off valve. Regulations in certain countries require automatic shut-off valves to be positioned proximate to the master tank 12 and the slave tank 14 that will automatically shut off in the event of a line rupture for safety purposes.
FIG. 2 is a schematic diagram of a known compressed hydrogen gas master/master tank system 64 that includes system components to address the requirement mentioned above. The tank system 64 includes two tanks 66 and 68 that may both be considered master tanks. Compressed hydrogen gas from the tank 66 for a fuel cell stack (not shown) is output on line 70 and compressed hydrogen gas from the tank 68 for the fuel cell stack is output on line 72. The lines 70 and 72 are combined into a single line 74. A high pressure regulator 76 is positioned in the line 70 for the tank 66, and a high pressure regulator 78 is positioned in the line 72 for the tank 68. Another pressure regulator 80 is positioned in the line 74 for a second pressure regulation step for both of the tanks 66 and 68. A filter 84 is provided in the line 70 to filter the hydrogen gas from the tank 66 and a filter 86 is provided in the line 72 to filter the hydrogen gas from the tank 68.
In this design, an electrically driven solenoid shut-off valve 88 is provided in the line 70 between the pressure regulators 76 and 80, and an electrically driven solenoid shut-off valve 90 is provided in the line 72 between the pressure regulators 78 and 80. The valves 88 and 90 are mid-pressure valves because they are positioned at a pressure location between the pressure regulators 76 and 78 and the second pressure regulator 80. Because the valves 88 and 90 are positioned at a location where the differential pressure across the valve 88 and 90 is relatively high, the electrical energy required to maintain the valves 88 and 90 in the open position against the differential pressure is also relatively high. If a leak or rupture occurs, the differential pressure across the shut-off valve will increase, and the electrically energy will not be enough to maintain the valve in the open position. Thus, it will automatically close. However, these high differential pressure shut-off valves add significant cost and complexity to the system 64. A low-pressure electrically driven solenoid shut-off valve 92 is positioned downstream of the pressure regulator 80.
The tanks 66 and 68 are refueled on line 94 through a refueling coupler 96. A filter 98 filters the hydrogen gas coming into the system 64. A check valve 100 in the line 94 prevents the hydrogen gas from the tanks 66 and 68 from going back through the coupler 96, and check valves 102 and 104 prevent the hydrogen gas from the tanks 66 and 68, respectively, from going into the other tank 66 or 68 on the line 94. A thermal activated pressure relief valve 106 is provided in a relief line 108 for the tank 66, and a thermal activated pressure relief valve 110 is provided in relief line 112 for the tank 68.